(6c) The SMSI Effect of Coox-Pt and Coox-Au Inverse Catalysts

Miquel Salmeron, Heath Kersell, Chen Hao Wu, Matthjis van Spronsen

Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA

Materials Science and Eng. Department, University of California, Berkeley, CA 94720, USA

The metal-support interaction (SMSI) is a topic investigated and debated for decades. It refers to the observation that catalyst particles supported on reducible oxides become covered, after oxidation and reduction activation, by a layer of oxide of the support metal that over the top of the catalyst. It is manifested by loss of chemisorption ability for CO and H₂, but also by an increase of reactivity for several reactions, particularly oxidation reactions. The widely accepted explanation is that new active sites have been formed at the interface between the oxide support and the catalyst particle. In these sites reactant species (e.g., CO and O in the CO oxidation reaction) adsorb and meet to form the product, the noble metal binding CO and the oxide providing O. However, this long-held assumption still lacks direct support from microscopy and spectroscopy, due in part to the difficulty to access peripheral sites at metal-oxide interface. I will present results from our laboratory using operando Scanning Tunneling Microscopy (STM) and X-ray Photolectron Spectroscopy (XPS), on an inverse support system where the noble metal is an atomically flat single crystal and oxide is deposited on top. Our observations support a model where the active sites are reduced metal atoms of the support in direct contact with the noble metal, independently of whether they are located at the edge or inside oxide islands.